Arrays of antennas, or array antennas, are used in many different applications, including radar systems. The principle figure of merit of an array antenna, is its signal to noise ratio, which is given by the radar range equation:
                                          S            N                    =                                                                      P                  T                                ⁢                                  G                  T                                                            4                ⁢                π                ⁢                                                                  ⁢                                  R                  2                                                      ·                          σ                              4                ⁢                π                ⁢                                                                  ⁢                                  R                  2                                                      ·                          A                                                Lk                  b                                ⁢                TB                                                    ,                            EQ        .                                  ⁢        1            where S=instantaneous signal power, N=noise power, PT=peak transmit power, GT=transmit antenna gain, R=range to target, σ=target radar cross section, A=antenna aperture area, L=losses, kb=Boltzmann's constant, T=effective receive noise temperature, and B=noise bandwidth.
A strategy for improving radar merit is to increase transmit power, PT. Increasing aperture size, A, is another strategy for increasing the signal to noise ratio of an array antenna. Increasing aperture size, while equally effective, can have practical limits especially in airborne applications because of the limited space and mass/weight restrictions. For example, high altitude airships typically have very strict limits on mass and every effort to reduce the mass of the antenna must be made; though the power consumed by an antenna often has an indirect impact effect on airship mass that is many times its direct contribution.
Real antennas have been shown to reach a minimum power and mass as aperture is increased. FIG. 1 depicts a graph 100 showing such a relationship for one previous study. The non-linear behavior indicated is believed to stem from at least two factors: (1) receiver power per antenna element remaining constant as aperture area is increased; and, (2) the mass of required cooling equipment (especially heat spreader mass) falling more slowing than the amount of power as aperture area is increased.